Development of a combined multi-spectral optoacoustic microscopy and optical coherence tomography imaging instrument for mapping multiple chromophores in biological tissues

This report presents a state-of-the-art multimodality imaging device that combines multi-spectral optoacoustic microscopy (OAM) and optical coherence tomography (OCT) to chart absorbers in live tadpoles (Xenopus laevis) accurately. The OAM channel captures maps of five internal contrast agents: melanin, haemoglobin, collagen, glucose, and lipids. A novel

method was developed to achieve this by assuming that each voxel in the 3D-OAM image exhibits a single chromophore

contributing to the optoacoustic signal. The device is powered by a single optical source (SuperK Compact, NKT

Photonics) that operates across an ultra-wide spectral range of 450 to 2400 nm. The set-up was optimized by minimizing optical aberrations and attenuation on optical components to stimulate the sample effectively. Using optical pulses of 2 ns duration and a repetition rate of 20 kHz, the device imaged tadpoles in their embryonic stage at multiple wavelengths, using narrow spectral windows of 25 nm bandwidth within the broad spectrum of the supercontinuum source at a time.

In addition, an ultra-high-resolution OCT imaging channel operating at 1300 nm (spectral bandwidth 180 nm) was created and incorporated into the device. The OCT channel, also powered by a commercial supercontinuum source (SuperK EXTREME EXR9, NKT Photonics), was used for guidance purposes and to help determine the location of the chromophores.